But here is the thing, if I copy the output from that same API url above and put it on my own server (and change my table definition to use it), things work just fine. I tried both with and without API key without any difference.

I can think of three options:

1) Something in Yahoo headers calling something in SO's engine to throw a dummy. I can't confirm it since it does not go via me (and I don't know of any Wireshark SAAS)

2) SO is explicitly blocking Yahoo/YQL services out of principle or due to quote overrun

If anybody can shed any light on this or share past experience, it would be appreciated. I think the full mapping of API would not be that big a task and would open interesting opportunities, but not if it is impossible to get past this first step.

Usually the client (Yahoo) would need to specify Accept-Encoding header to support gzip format. I don't think the server would send compressed content otherwise. At least that's the theory. Can't see the headers, can't confirm.
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Alexandre RafalovitchAug 13 '10 at 4:59

2

@Alex - the API will send you gzipped content, even if you don't request it.
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Mark HendersonAug 13 '10 at 5:18